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Review

Epipolythiodioxopiperazines: From Chemical Architectures to Biological Activities and Ecological Significance—A Comprehensive Review

by
Qingqing Zhang
1,†,
Mingyang Jia
1,†,
Hongyi Li
1,
Tingting Shi
1,
Ying Xu
1,
Taili Zhao
1,
Lixin Zhang
1,2,
Peipei Zhao
1,* and
Xuekui Xia
1,*
1
Biology Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250103, China
2
State Key Laboratory of Bioreactor Engineering, School of Biotechnology, East China University of Science and Technology, Shanghai 200237, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Fermentation 2025, 11(12), 700; https://doi.org/10.3390/fermentation11120700
Submission received: 8 November 2025 / Revised: 12 December 2025 / Accepted: 15 December 2025 / Published: 17 December 2025
(This article belongs to the Section Microbial Metabolism, Physiology & Genetics)
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Abstract

Epipolythiodioxopiperazines (ETPs), characterized by a diketopiperazine (DKP) core bridged by disulfide or polysulfide bonds, exhibit exceptional structural diversity and functional adaptability. This review comprehensively explores their multifaceted properties, covering chemical structural characteristics, therapeutic application potential, and ecological functional value. Structural diversity arises from variations in the core DKP scaffold, sulfur bridge connectivity patterns, and additional modifications. Biosynthesis involves initial DKP assembly, enzyme-catalyzed sulfur incorporation and oxidation to form the signature sulfur bridge of ETPs, diversification by tailoring enzymes, and distinct regulatory mechanisms. ETPs possess diverse biological activities, including cytotoxicity, antitumor activity, antimicrobial properties, and immunomodulatory functions. From an ecological standpoint, ETPs mediate fungal–host interactions and influence competition and symbiosis within fungal communities. Furthermore, this review also addresses the current challenges and outlines future research directions. In summary, as a class of significant compounds spanning the fields of chemistry, biology, medicine, and ecology, ETPs deserve focused attention for their research value and application prospects.

Graphical Abstract

1. Introduction

Natural products have long served as a cornerstone of leading drug candidates in drug discovery, owing to their unparalleled structural diversity and excellent biocompatibility [1]. Over the past decades, microbial bioactive natural products served as a vital molecular source for modern drug development. Currently, approximately 50% of approved small-molecule drugs are either natural products, their derivatives, or structural analogs [1,2]. Epipolythiodioxopiperazines (ETPs) represent a major family of natural diketopiperazine alkaloids, predominantly classified as fungal secondary metabolites. Their defining structural features consist of a core diketopiperazine (DKP) scaffold, biosynthetically derived from two amino acids, and a characteristic internal epipolysulfide bridge, which may be a disulfide or polysulfide [3,4,5] (Figure 1). Ever since gliotoxin was first isolated as a representative ETP, an increasing number of structurally distinct ETPs have been discovered and characterized from diverse fungi. This review aims to offer comprehensive and novel insights into ETPs, covers aspects such as their structural diversity, biosynthetic mechanisms, biological activities, and potential applications.

2. The Structural Diversity of ETPs

ETPs are characterized by two defining structural features: a core 2,5-diketopiperazine (DKP) scaffold and characteristic sulfur bridges, typically disulfide bonds, though polysulfide linkages also exist [6,7]. The DKP scaffold is biosynthesized in fungi primarily via the nonribosomal peptide synthetase (NRPS) pathway, which catalyzes the condensation of two α-amino acids, at least one usually being aromatic (such as phenylalanine, tyrosine, or tryptophan) [8]. NRPSs often cluster with tailoring enzymes, such as oxidoreductases, cytochrome P450 enzymes, methyltransferases, and prenyltransferases. These post-modification processes introduce specialized functional groups into the core scaffold, enhancing pharmacological potency and expanding the structural and functional diversity of natural products [9].
Sulfur, existing in various oxidation states (ranging from −2 to +6), is a prevalent heteroatom in medicinal chemistry and is incorporated into numerous biologically profound molecules. It participates in the formation of diverse functional groups, including thioethers, sulfoxides, sulfones, sulfonamides, sulfamates, and sulfonic acids [10]. In comparison with oxygen, sulfur possesses a larger atomic radius, more diffuse electronic orbitals, and appreciably lower electronegativity. These properties enable its application in drug design to modulate the potency of small-molecule therapeutics toward biological targets. Through bioisosteric replacement, pharmacophore modification, and influence on pharmacological properties as well as metabolic stability, sulfur significantly impacts drug activity [10]. Currently, sulfur constitutes a functional group component in approximately 25% of the top 200 small-molecule drugs in 2020. Between 2017 and 2021, almost 30 sulfur-containing drugs were approved by the U.S. Food and Drug Administration (FDA), highlighting the importance of sulfur in drug design [10]. ETPs are characterized by a six-membered DKP ring, wherein the disulfide (-S-S-) or polysulfide functional group serves as the critical moiety for their bioactivity. The complete removal or cleavage of the sulfur bridge, or the addition of reducing agents (e.g., dithiothreitol), typically results in total loss of biological activity [11]. The toxicity of ETPs is primarily attributed to their disulfide bonds, which can inactivate proteins through reactions with thiol groups as well as their capacity to generate reactive oxygen species (ROS) via redox cycling [6]. This mechanism is well exemplified by gliotoxin, one of the most extensively studied ETP mycotoxins. Its defining structural feature is a disulfide bridge that spans the diketopiperazine ring, which is central to its toxic effects. This bridge enables covalent cross linking with cellular proteins via cysteine residues and participates in a continuous redox cycle, alternating between the reduced dithiol and oxidized disulfide states. This process generates deleterious reactive oxygen species and is widely accepted as a key mechanism underlying its toxicity. Thus, the potent toxicity shared across the ETP class fundamentally arises from this dual mechanism of thiol modification and oxidative stress [12].
To date, over 60 ETPs containing 1 to 4 sulfur atoms in the form of disulfide/polysulfide bridges, thioether linkages, or methoxythio groups have been isolated and structurally characterized [13].

2.1. Core Diketopiperazine Scaffold and Sulfur Bridge Connectivity

The DKP scaffold, formed by the cyclocondensation of two α-amino acids, represents the smallest cyclic dipeptide with a rigid six-membered piperazine ring. Its unique modification by sulfur bridges generates a key pharmacophore in bioactive natural products [14]. The structural diversity of ETPs is largely attributed to the combination of different α-amino acids (such as phenylalanine, tryptophan, and tyrosine) in the DKP scaffold, variations in the attachment sites of disulfide bonds, and post-modifications.
Based on the position of sulfur atom linkage to the DKP ring, ETPs can be classified into two subfamilies: the α, α’-disulfide-bridged (C2-C2′) and α, β’-disulfide-bridged (C2-C3′) subtypes [15] (Figure 2). Previously reported α, α′-disulfide-bridged ETPs include gliotoxin (cyclo-L-Phe-L-Ser) [16], sirodesmin PL (cyclo-O-dimethylallyl-L-Tyr-L-Ser) [17], acetylaranotin (cyclo-L-Phe-L-Phe) [18], and sporidesmin A (cyclo-L-Trp-L-Ala) [15,19]. In contrast, only a limited number of α, β′-disulfide-bridged ETPs have been characterized, such as pretrichodermamide A (cyclo-L-Phe-L-Phe) [9], aspirochlorine (cyclo-L-Phe-L-Phe) [20], lasiodipline D (cyclo-L-Trp-L-Ala) [21], and gliovirin (cyclo-L-Phe-L-Phe) [22], which exhibit more complex and uncommon sulfur-bridge connectivity patterns. The sulfur bridge constitutes the defining structural determinant of ETPs, maintaining stability, regulating bioactivity, and governing the distinctive characteristics that underpin their pharmacological efficacy and drug potential [23]. Specifically, the sulfur-bridged structure confers three key properties to ETPs. First, it enhances molecular stability. For instance, α, α′-bridged isomers such as α-pretrichodermamide A exhibit greater kinetic stability compared to their α, β′-bridged counterparts due to a higher activation energy barrier, whereas α, β′-bridged pretrichodermamide A rapidly desulfurizes and degrades under basic conditions [24]. Second, it ensures structural rigidity, which is essential for biological function [23]. As seen in 6-acetylmonodethiogliotoxin from the marine fungus Dichotomomyces cejpii, the sulfur bridge connects key sites on the dioxopiperazine ring, stabilizing the molecular conformation and thereby enabling its anti-inflammatory and NF-κB inhibitory activities [25]. Third, it imparts distinctive and potent bioactivity, making ETPs valuable for pharmaceutical applications [26]. For example, 6-deoxy-5a,6-didehydrogliotoxin from the marine fungus Penicillium sp. shows strong inhibitory activity against P388 leukemia cells with a half maximum inhibitory concentration (IC50) of 0.058 μmol/L, an effect entirely dependent on the sulfur bridge [27]. Similarly, 7-dehydroxyepicoccin H from the deep-sea fungus Epicoccum nigrum SD-388 exhibits antibacterial activity against aquatic pathogens such as Vibrio vulnificus, Vibrio alginolyticus, and Edwardsiella tarda with minimum inhibitory concentration (MIC) values of 4.0–8.0 μg/mL, which is also directly reliant on the sulfur bridge, as desulfurized analogs lose this activity [28]. Collectively, these roles make the sulfur bridge indispensable for the unique physicochemical profile and drug development potential of ETPs.

2.2. Other Structural Modifications

In addition to disulfide bridges, the structural diversity of ETPs requires coordinated actions of various post-modification enzymes. These modifications occur on both the core DKP scaffold and amino acid side chains, including methylation, acetylation, hydroxylation, prenylation, halogenation, cyclization, and truncation reactions [4]. These modifications serve as key regulators of ETPs’ bioactivities such as antibacterial, antitumor, and immunosuppressive effects, by altering compound lipophilicity, polarity, and target interactions.
The enzymes involved in the diverse modifications of ETPs primarily include cytochrome P450 enzymes responsible for hydroxylation reactions [29], methyltransferases utilizing S-adenosyl-L-methionine (SAM) as the methyl donor [30], prenyltransferases catalyzing prenylation reactions [31], and halogenases responsible for the incorporation of halogen atoms (Cl, Br, I) [32]. These enzyme classes act collaboratively on distinct sites, following specific temporal and spatial sequences. Together, they shape the expansive chemical space of ETPs, forming the molecular basis for their diversity in bioactivity.

3. Biosynthesis of ETPs

3.1. Initial Step: Assembly of the DKP Skeleton

The biosynthesis of ETPs begins with the assembly of the DKP scaffold. In fungi, this cyclic dipeptide is predominantly synthesized by NRPSs [9]. NRPSs are composed of multiple modules, with distinct domains within each module catalyzing various biochemical reactions, including substrate recognition and loading, peptide chain elongation, and product release [33]. The core NRPS module consists of the adenylation (A) domain, thiolation (T)/peptidyl carrier protein (PCP) domain, and condensation (C) domain [34] (Figure 3A). The A domain recognizes natural or unnatural amino acids (e.g., L-Trp, L-Leu, β-OH-Tyr, 3-OH-Pro) and consumes ATP to generate a high-energy aminoacyl-AMP intermediate, releasing pyrophosphate (PPi). Through shared active site residues (e.g., Lys and Asp), the A domain specifically binds substrates. Its substrate promiscuity enables the recognition of diverse amino acid derivatives, providing the foundation for DKP scaffold diversity [33,35]. The C domain catalyzes the nucleophilic substitution reaction between the aminoacyl thioester on the current module’s T domain and the peptidyl thioester from the upstream module to form a peptide bond. This domain facilitates nucleophilic attack of the amino group on the carboxyl group through conserved catalytic motifs (e.g., HHxxxDG), enabling stepwise peptide chain elongation [33,36]. The thioesterase (TE) domain or fungal-specific terminal C-like domains (CT) domain catalyzes the intramolecular cyclization of dipeptide intermediates via amino group attack on the carboxyl group, forming the six-membered DKP scaffold. The TE domain hydrolyzes the thioester bond via hydrolysis or nucleophilic attack to release free DKP molecules, while in fungi, the CT domain may substitute for TE function to directly mediate cyclization [33]. Additionally, NRPSs also contain various modification domains, such as the epimerization (E) domain, methylation (MT) domain, heterocyclization (Cy) domain, and formylation (F) domain [37]. E domains, commonly found in NRPSs producing D-amino acid-containing peptides, convert L-amino acids to D-amino acids. These domains share homology with C domains and contain conserved His and Glu residues in their active sites, utilizing acid-base catalysis to invert amino acid configuration [38]. MT domain recognizes SAM and substrates through conserved sequences, using SAM as a coenzyme to mediate N-methylation of peptide backbones or side chains, thereby enhancing product stability or bioactivity [33,39]. The Cy domain evolved from C domain, with its active site harboring a DxxxxDxxS motif that promotes nucleophilic attack by hydroxyl or sulfhydryl groups on peptide bonds, thereby catalyzing the formation of heterocycles (e.g., thiazoline, oxazoline) from serine or cysteine residues [33]. Finally, the released NRPS products undergo further modifications by other enzymes encoded by genes adjacent to NRPS gene to generate the final metabolites.
The extensively studied gliotoxin-class compounds are synthesized via the condensation of L-phenylalanine (L-Phe) and L-serine (L-Ser) catalyzed by the NRPS GliP to form a cyclic dipeptide scaffold [40]. GliP is a three-module NRPS (arranged as A1-T1-C1-A2-T2-C2-T3), where two A domains selectively activate L-Phe and L-Ser, respectively [41,42]. Sirodesmin PL, the first ETP with a predicted biosynthetic gene cluster (in 2004), is encoded by the 18-gene sir cluster [43]. Within this cluster, sirP encodes the bimodular NRPS SirP (A1-T1-C1-A2-T2-C2), which is proposed to catalyze the condensation of 4-O-dimethylallyl-L-tyrosine and L-Ser into a cyclic dipeptide [17,43]. SirP is essential for initiating sirodesmin PL biosynthesis by assembling amino acid precursors into the peptide backbone structure. Chetomin, a rare heterodimeric indole alkaloid with an unsymmetrical structure featuring a distinctive N-C bond linkage [44]. Its biosynthetic gene cluster contains 18 genes, including cheP, which encodes a NRPS (A1-T1-C1-A2-T2-C2-T3) responsible for the condensation of L-tryptophan (L-Trp) and L-Ser to form a cyclic dipeptide intermediate, constituting a foundational step in constructing chetomin’s heterodimeric indole scaffold [44] (Figure 3B).
As the key enzyme in the multi-step biosynthesis of ETPs, NRPS catalyzes amino acid activation, condensation, cyclization, and modification through the synergistic action of domains such as A, C, T, and TE/CT, ultimately generating the DKP scaffold and its derivatives. The diversity and complexity of their catalytic functions provide vast potential for structural modification of natural products and novel drug development.

3.2. Sulfur Incorporation and Oxidation

Following the formation of the DKP scaffold, sulfur incorporation and oxidation constitute the critical steps determining the formation of characteristic transannular disulfide bonds in ETPs, which directly influence their structural diversity and bioactivity. Taking gliotoxin as an example, during its biosynthesis, the cytochrome P450 monooxygenase GliC first catalyzes the α, α’-hydroxylation of the DKP core, generating reactive sites for thiol nucleophilic substitution [45,46] (Figure 4). Subsequently, the glutathione-S-transferase GliG catalyzes the sulfuration reaction. GliG recognizes and binds to the dihydroxylated DKP, facilitating nucleophilic substitution of the α-hydroxyl groups on the Phe and Ser residues of DKP by the thiol group of glutathione (GSH) (a sulfur-containing tripeptide composed of cysteine, glutamate, and glycine [47]), thereby completing the first sulfur incorporation and forming a diglutathionyl conjugate with C-S bonds [48]. A subsequent tri-enzyme cascade comprising γ-glutamyltranspeptidase GliK, carboxypeptidase GliJ, and PLP-dependent β-lyase GliI degrades the GSH conjugates, releasing a free α, α′-dithiol intermediate with thiol groups covalently attached at the α- and α′-carbons of the DKP core. This intermediate serves as the substrate for subsequent oxidative bond formation [40]. The flavin-containing oxidase GliT is the key enzyme responsible for catalyzing the conversion of the α, α’-dithiol intermediate into an α, α’-disulfide bond. Its activity depends on a conserved CXXC motif (e.g., the 145–148 amino acid sequence CLFC) [15]. The reaction initiates with the deprotonation of one thiol group, generating a thiolate anion that attacks the CXXC disulfide in GliT to form an enzyme-substrate mixed disulfide intermediate. Subsequently, the oxidized form of flavin adenine dinucleotide (FAD, Flox) accepts electrons at the C4a position, promoting oxidative coupling of the second thiol group. This ultimately yields an α, α’-disulfide bond bridging the DKP ring [15].
In pretrichodermamide A, the sulfur incorporation process introduces β’-position modifications based on the α, α’-bridged framework. Initially, the NRPS TdaA catalyzes the formation of a Phe-containing cyclic dipeptide scaffold. Subsequently, the cytochrome P450 monooxygenase TdaS is proposed to putatively mediate hydroxylation at the α, α′ and β′ positions of this scaffold [49]. Similarly to α, α′-disulfide-bridged ETPs, GSH serves as the sulfur donor and is progressively degraded via a four-enzyme cascade (TdaL/TdaV/TdaJ/TdaT), yielding an intermediate containing both α, α′-dithiol and a, β′-hydroxyl groups [15]. Notably, β′-hydroxylation is frequently accompanied by O-acetylation (catalyzed by TdaF), providing the structural basis for subsequent disulfide bond migration. The flavoenzyme TdaE, harboring the CMYQ motif, drives this migration through the generation of an ortho-quinone methide (o-QM) intermediate. Specifically, the Gln140 residue of TdaE deprotonates the β-carbon adjacent to the β′-acetoxy group, generating a highly electrophilic o-QM species. The quinoid structure of o-QM facilitates nucleophilic attack by the α′-thiol group at the β′-carbon, concomitant with ring-opening of the transient thiirane intermediate. This cascade ultimately forms the α, β′-disulfide bond and constructs the spirofuran ring system [50]. Sulfur incorporation and oxidation represent critical pivotal steps in ETP biosynthesis, highlighting the intricate enzymatic regulation of sulfur bond formation in nature.

3.3. Tailoring Enzymes and Their Roles in Structural Diversification

Following the establishment of the sulfur-bridged DKP core, the biosynthetic pathways of ETPs are further diversified by a suite of tailoring enzymes (Figure 5). Among these, cytochrome P450 monooxygenases play a pivotal role by catalyzing site-selective hydroxylation, typically introducing hydroxyl groups at specific carbon positions on either the DKP ring or amino acid side chains [51]. Such hydroxylation modification can significantly modulate the polarity, water solubility, and stability of ETPs, while also influencing their reactivity and bioactivity [29]. A prime example is the cytochrome P450 monooxygenase TdaS in Trichoderma hypoxylon, which functions as a key early-stage enzyme in the biosynthesis of the α, β’-disulfide-bridged ETP pretrichodermamide A. The core function of TdaS is to oxidize the foundational cyclodipeptide scaffold, cyclo-L-Phe-L-Phe (cFF), at its α, α’, and β’ positions. This oxidation generates a polyhydroxylated cFF intermediate, which is indispensable for subsequent biosynthetic steps: it provides reactive hydroxyl groups for GSH addition, enables the formation of carbon-sulfur bonds during GSH degradation, and lays the structural basis for transannular disulfide (α, α’- or α, β’-disulfide) formation. Additionally, the polyhydroxylated intermediate produced by TdaS supports the biosynthesis of diverse ETP derivatives by offering sites for further modifications such as thiomethylation [7,50].
Methyltransferases catalyze methylation reactions by transferring methyl groups from SAM to specific atoms (e.g., C, O, N, or S nucleophilic centers) in ETPs, thus influencing the lipophilicity, binding affinity, and pharmacokinetic properties of ETPs, and significantly alter their biological activities [30]. For instance, GliN-mediated N-methylation in gliotoxin suppresses the spontaneous formation of polysulfide compounds and is essential for its cytotoxicity: N-demethylation product exhibits a 100-fold reduced activity [30,31,52,53,54]. Beyond N-methylation, O-methyltransferases also critically tailor ETP structure and function. A prominent example is TdaH from T. hypoxylon, which catalyzes C6’-O-methylation of α, β’-disulfide ETP precursors. This key step provides the structural basis for disulfide migration and 1,2-oxazine ring formation. Ecologically, this methylation enhances the fungus’s antagonism in a pathogen-specific manner, significantly boosting inhibition against Botrytis cinerea and Aspergillus parasiticus but not Fusarium nivale, a finding confirmed by gene deletion and quantitative analysis. Furthermore, TdaH shows strong co-evolution (R = 0.5307, p = 0.001) with cytochrome P450 TdaG across 17 ETP biosynthetic gene clusters, underscoring their synergistic role in biosynthesis [55]. Fungi employ S-methyltransferases to achieve self-protection via thiomethylation, a mechanism that balances redox homeostasis and avoids autotoxicity. For example, TmtA (or GtmA) from Aspergillus fumigatus mediates sequential methylation of gliotoxin’s C10a-SH and C3-SH groups, generating an inactive bis(methylated) product. This process blocks redox cycling and protein binding, and eliminating toxicity, thereby demonstrating precise methylation regioselectivity [56]. Methyltransferases thus mediate structural diversification, metabolic regulation, and self-protection in natural product biosynthesis, with their substrate specificity and catalytic mechanisms serving as key targets for drug design (e.g., ETP derivative development) and strain engineering (high-yield or novel compound biosynthesis).
Prenyltransferases catalyze prenylation reactions, which attach isoprenyl units (e.g., dimethylallyl) to specific sites of ETP substrate molecules via the formation of C-C bonds or C-heteroatom (O, N, S) bonds, with common attachment sites including hydroxyl groups, sulfhydryl groups, and indole rings (at C- or N- positions) [17]. The introduction of prenyl groups in natural products not only enriches the structural diversity of natural products, but also enhances the affinity with drug targets and bioavailability due to the increase in lipophilicity, and improves drug metabolism and pharmacokinetic properties [57,58]. For example, the tyrosine O-prenyltransferase SirD in sirodesmin PL biosynthesis demonstrates broad substrate specificity and regioselectivity, not only initiating biosynthesis via tyrosine O-prenylation but also enabling extensive prenylation of hydroxyl, sulfhydryl groups, and indole rings (at C- and N-positions). This significantly expands the application potential of prenylation in drug precursor synthesis and biocatalysis [59]. Owing to these versatile functions, the core applications of prenyltransferases are currently concentrated in drug development, natural product synthesis, industrial biocatalysis, and synthetic biology. They have become important tools in biomanufacturing and pharmaceutical research and are expected to further expand into new materials and green chemistry [58].
Halogenases introduce halogen atoms (e.g., Br, I) at specific positions of ETP molecules, enhancing target binding through electronic effects or steric hindrance [32], and can induce marine fungi to produce halogenated metabolites via media supplementation strategies. For example, the marine-derived fungus Trichoderma sp. TPU199 can produce the chlorinated derivative DC1149B in media containing NaCl, the brominated derivative DC1149R in media containing NaBr, and a new iodinated derivative iododithiobrevamide in media containing 3.0% NaI [32,60]. The introduction of halogen atoms affects the activity of compounds; for instance, the PTP1B inhibitory activity of brominated agelasine G is significantly stronger than that of its debrominated analog [32,61].
Acetyltransferases catalyze acetylation reactions, in which acetylation primarily targets hydroxyl or amino groups (especially lysine), and introduces acetyl moieties (CH3CO-) that significantly modulate molecular polarity, spatial conformation, and protein interactions [62,63]. For example, C11-hydroxyl acetylation in verticillin H alters its physicochemical properties and pharmacokinetics while preserving or even enhancing inhibitory activity against multiple cancer cell lines [64].
Furthermore, cyclizing enzymes catalyze ring-forming reactions that introduce additional rings, increasing structural complexity. Truncation reactions remove moieties, potentially generating smaller yet still bioactive derivatives. Collectively, these diverse post-modifications contribute to the structural diversity of ETPs and significantly modulate their biological activities.

3.4. Regulation of ETP Biosynthesis

The biosynthetic regulation of ETPs is a hierarchical, multifactorial process. In general, secondary metabolites are governed by biosynthetic gene clusters, and variations in gene expression levels can lead to differences in the quantity or type of secondary metabolites produced. The synthesis of secondary metabolites is a complex process regulated by multiple factors, including the coordinated action of various enzymes and transcription factors [65]. For instance, bis(methylthio)gliotoxin, a product of methyltransferase, can suppress the expression of ETP biosynthetic gene cluster, establishing a negative metabolic feedback loop to prevent excessive synthesis and subsequent toxicity accumulation, thereby modulating metabolism [56]. Transcriptional regulation plays a pivotal role, as specific transcription factors can bind to the promoter regions of genes involved in ETP biosynthesis, either activating or repressing transcription. In gliotoxin biosynthesis, the regulation of gli gene cluster is controlled by diverse proteins, including transcription factors, chromatin-associated factors, the MAP kinase MpkA, developmental regulators, and G-protein signaling modulators [66]. The Zn2Cys6 transcription factor GliZ acts as a key positive regulator, governing transcription of the entire gliotoxin biosynthetic gene cluster [12,67]. Overexpression of gliZ enhances gliotoxin and its derivatives accumulation, whereas gliZ deletion abolishes gliotoxin production [68]. RglT, a GAL4-like Zn(II)2Cys6 transcription factor, primarily controls gliT and gtmA expression [69]. It plays a role in oxidative stress resistance, gliotoxin biosynthesis, and self-protection. RglT directly binds promoters of gliZ, gliM, gliA, gliF, and gliT, regulating gene expression and thereby modulating gliotoxin biosynthesis [70].
In addition to transcriptional regulation, ETP biosynthesis is synergistically influenced by environmental factors and metabolic control. Key parameters during fungal cultivation, including nitrogen and carbon sources, pH, temperature, and aeration, all significantly impact secondary metabolite production [65]. For example, in the biosynthesis of cFF, a bioactive dipeptide with hepatoprotective, antidepressant, and anticancer activities that serves as a precursor for drugs such as gliovirin and penisuloxazin A, the CD-ST medium containing casamino acids as an organic nitrogen source enhances cFF synthesis [71]. This occurs through induction of NRPS gene expression (e.g., penP1) or direct supply of Phe precursors, thereby achieving a cFF yield of up to 295.25 mg/L. In contrast, the CD-G medium, which uses glucose as the carbon source and nitrate as the nitrogen source, relies on fungal endogenous Phe biosynthesis, yielding only 201.54 mg/L of cFF [71]. Aeration conditions also modulate fungal aerobic metabolism. For instance, in bioreactors, optimizing dissolved oxygen (pO2 at 30% saturation) and agitation speed (200–500 rpm) may enhance energy supply through the tricarboxylic acid (TCA) cycle and electron transport chain, thereby providing ATP for energy-demanding reactions (e.g., peptide bond formation) catalyzed by NRPS and significantly improving ETP biosynthetic efficiency [71].
Endogenous metabolic regulation also plays a pivotal role. Under natural conditions, the intracellular concentration of aromatic compounds in microbial cells is notably low, which fails to meet the demands of industrial fermentation. In microorganisms, the biosynthesis of aromatic compounds relies on core metabolic pathways, including the Embden-Meyerhof-Parnas (EMP) pathway, pentose phosphate pathway (PPP), and shikimate pathway. The shikimate pathway utilizes phosphoenolpyruvate (PEP) and erythrose-4-phosphate (E4P) as precursors to synthesize 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP), which is subsequently converted into chorismate through a series of enzymatic reactions [72]. Chorismate serves as the pivotal branch point in the biosynthesis of the three aromatic amino acids, L-Phe, L-Tyr, and L-Trp, as well as intermediates like 3-dehydroshikimate (DHS) that can be further metabolized into diverse aromatic derivatives [72,73]. Metabolic pathway engineering based on the “Influx-Throughput-Regulation-Blockage-Efflux” strategy has been proven effective. These include: (1) enhancing metabolic flux and precursor supply (Influx); (2) relieving feedback inhibition and activating key enzymes (Throughput); (3) regulating or attenuating competing branch pathways (Regulation); (4) blocking product degradation pathways (Blockage); and (5) promoting product efflux to alleviate feedback inhibition (Efflux) [72,74]. For example, the NRPS gene penP1 was identified in Penicillium and heterologously expressed in Aspergillus nidulans to construct a cFF-producing strain. By deleting phenylalanine ammonia lyase (PAL) gene, particularly PAL2, the consumption of Phe precursors was reduced, elevating the cFF yield from 295.25 to 326.79 mg/L. Furthermore, overexpression of key enzymes like DAHP synthase and chorismate mutase in feedback-insensitive mutants further enhanced cFF production [71].

4. The Biological Activity of ETPs

4.1. Cytotoxicity and Antitumor Activity

Many ETPs exhibit significant cytotoxicity toward cancer cells, positioning them as potential candidates for antitumor drugs (Table 1). For instance, gliotoxin has been reported to exert anticancer effects by inducing apoptosis in various human cancer cell lines [53]. Recent studies show that gliotoxin potently inhibits both monolayer and spheroid cultures of diverse breast cancer subtypes (e.g., MDA-MB-231, MDA-MB-468, MCF-7, IC50 = 0.1457–1.538 μM), demonstrating robust anticancer properties [75]. Chetomin effectively targets both cancer stem cells (CSCs) and non-stem cells in non-small cell lung cancer (NSCLC) by inhibiting the Hsp90/HIF1α pathway, suppressing proliferation and inducing apoptosis, the corresponding IC50 values are 1.6–22 nM for NSCLC CSCs and 4.1–6.3 nM for NSCLC non-CSCs [76,77]. Furthermore, by disrupting the interaction between HIF-1α and p300, chetomin downregulates hypoxia-responsive genes, thereby inhibiting multiple myeloma cell growth (IC50 = 4.1 nM) and enhancing the antitumor efficacy of conventional chemotherapeutic agents [78]. Chaetocochin J, isolated from Chaetomium sp., is a promising candidate for colorectal cancer treatment, exhibiting potent inhibitory effects on colorectal cancer cell proliferation (IC50 = 0.5 μM). It induces apoptosis more effectively than topotecan and activates autophagy, with its mechanism of action involving the AMPK and PI3K/AKT/mTOR signaling pathways [79].
The pretrichodermamide derivatives exhibit potent cytotoxicity by interfering with essential cellular processes, particularly through induction of cell cycle arrest at specific checkpoints to inhibit cancer cell division and proliferation. For example, pretrichodermamide B, isolated from Trichoderma longibrachiatum, functions as a novel STAT3 inhibitor targeting the canonical JAK/STAT3 signaling pathway [80]. It directly binds to STAT3, inhibiting its phosphorylation and thereby suppressing cancer cell proliferation, inducing G2-phase cell cycle arrest, and promoting apoptosis. This is evidenced by its cytotoxic activity against a panel of cancer cell lines, with IC50 values of 5.28 μM to 6.57 μM for lung cancer cells A549, 2.45 μM for prostate cancer cells DU145, and 5.30 ± 1.07 μM for colorectal cancer cells HCT116. In vivo studies showed that intraperitoneal administration at 10 mg/kg significantly reduced A549 xenograft tumor growth by approximately 40% [80,81].
Some ETPs enhance their antitumor potency by inhibiting enzymes involved in DNA replication and repair. For example, TAN-1496 A, isolated from Microsphaeropsis sp., is a highly specific inhibitor of calf thymus DNA topoisomerase I (Topo I). It potently inhibits Topo I relaxation activity in a dose-dependent manner without affecting Topo II even at high concentrations, underscoring its potential as a targeted antitumor agent. This compound significantly suppresses the growth of multiple murine and human tumor cell lines (IC50 = 0.016–0.072 μg/mL), inducing DNA fragmentation and apoptosis [82,83]. TAN-1496 A significantly expands the known bioactivity spectrum of Microsphaeropsis nitrogenous metabolites and underscores the potential of this fungal source for discovering targeted antitumor agents.
Table 1. Cytotoxicity and antitumor activity of ETPs.
Table 1. Cytotoxicity and antitumor activity of ETPs.
CompoundBiological ActivityIC50Refs.
Gliotoxinbreast cancer subtypesIC50 = 0.1457–1.538 μM[75]
ChetominNSCLC CSCsIC50 = 1.6–22 nM[77]
NSCLC non-CSCsIC50 = 4.1–6.3 nM[77]
multiple myeloma cellIC50 = 4.1 nM[78]
Chaetocochin Jcolorectal cancer cellIC50 = 0.5 μM[79]
Pretrichodermamide Blung cancer cells A549IC50 = 5.28–6.57 μM[80]
prostate cancer cells DU145IC50 = 2.45 μM
colorectal cancer cells HCT116IC50 = 5.30 ± 1.07 μM
TAN-1496 Amurine and human tumor cell linesIC50 = 0.016–0.072 μg/mL[82]

4.2. Antimicrobial Activity

ETPs also exhibit significant antimicrobial properties (Table 2). Key mechanisms include redox-mediated generation of ROS, induction of membrane lipid peroxidation, and formation of mixed disulfide bonds with cysteine sulfhydryl groups in proteins, collectively leading to bacterial cell death (e.g., via programmed necrosis or membrane lysis) [6]. For example, verticillin D exhibits antibacterial activity against Staphylococcus aureus with an MIC value ranging from 3 to 10 μg/mL, which is comparable to that of the positive control, gentamicin sulfate [84,85]. Glionitrin A displays remarkable antibacterial activity against methicillin-resistant S. aureus (MRSA) (MIC = 0.78 μg/mL) [86]. Another notable example is Chetracin B, a bis(methylthio)piperazinedione-type ETP isolated from diverse fungal sources including the Antarctic fungus Oidiodendron truncatum GW3-13 and the marine-derived fungus Westerdykella reniformis [87,88]. Chetracin B exhibits potent activity against drug-resistant Gram-positive bacteria, particularly MRSA, with an MIC of 0.7 µM and an IC50 of 0.2 µM surpassing the efficacy of vancomycin (MIC = 1.4 µM, IC50 = 0.6 µM). It also shows activity against vancomycin-resistant Enterococcus (VRE), though weaker than rifampicin [89,90]. Its antimicrobial action is structurally supported by the presence of polysulfide bridges, which facilitate redox-mediated ROS generation and mixed disulfide bond formation with bacterial proteins [90].
ETPs also act as antifungal agents by potentially disrupting fungal cell wall biosynthesis or arresting the fungal cell cycle. For instance, chetomin exhibits broad-spectrum antibacterial and antifungal activities. The MIC of chetomin against Candida albicans sc5314, C. albicans 17#, and C. albicans g5, were 1.56, 3.125, and 3.125 μg/mL, respectively. Its anti-MRSA activity (MIC = 0.05 μg/mL) is significantly stronger than that of vancomycin and methicillin, while also demonstrating inhibitory activity against Bacillus subtilis, highlighting its potential as a novel antimicrobial agent [44,91]. Acetylgliotoxin, isolated from the culture products of the marine fungus Aspergillus pseudofischeri in GluPY medium [92], exhibits inhibitory activity against C. albicans (MIC = 2.0 μg/mL) and Cryptococcus neoformans (MIC = 4.0 μg/mL) [93]. Aspirochlorine, derived from Aspergillus flavus, demonstrates potent inhibitory activity against azole-resistant C. albican (IC50 = 0.028 μM) [26].
Table 2. Antimicrobial activity of ETPs.
Table 2. Antimicrobial activity of ETPs.
Compound NamePathogensMIC/IC50Refs.
Verticillin DS. aureusMIC = 3–10 μg/mL[85]
Glionitrin AMRSAMIC = 0.78 µg/mL[86]
Chetracin BMRSAMIC = 0.7 µM, IC50 = 0.2 µM[89]
ChetominC. albicans
MRSA		MIC = 1.56–3.125 μg/mL
MIC = 0.05 µg/mL		[44]
AcetylgliotoxinC. albicans
C. neoformans		MIC = 2.0 µg/mL
MIC = 4.0 µg/mL		[93]
Aspirochlorineazole-resistant C. albicansIC50 = 0.028 µM[21]

4.3. Immunomodulatory Activity

Certain ETPs exhibit significant immunomodulatory properties, with gliotoxin representing one of the most extensively studied immunosuppressive members of this class. Gliotoxin exerts broad and potent immunosuppressive effects through multiple mechanisms. A well-established pathway involves the inhibition of NF-κB activation by blocking I-κB degradation, thereby preventing the nuclear translocation of NF-κB and suppressing the expression of downstream pro-inflammatory genes [12,94]. Beyond this, gliotoxin profoundly impairs innate immune cell functions. It inhibits neutrophil chemotaxis, phagocytosis, and the critical respiratory burst by interfering with NADPH oxidase assembly and electron transfer and reduces neutrophil recruitment by suppressing leukotriene B4 production via inhibition of LTA4H. Furthermore, gliotoxin induces apoptosis in alveolar macrophages via a ROS- and Bak-dependent pathway and also promotes T-cell apoptosis while inhibiting their activation and IFN-γ production. B-cell function is similarly suppressed through NF-κB inhibition [12]. Other ETPs also demonstrate notable immunomodulatory activity. Both chetomin and chetoseminudin A, isolated from the ascomycete fungi Chaetomium seminudum and Chaetomium globosum, exert potent immunosuppressive activity by inhibiting the proliferation of mouse splenic lymphocytes. They have identical IC50 value of 0.24 nmol/mL against Con A-induced T-cell proliferation, and chetomin displays a slightly stronger inhibitory effect on LPS-induced B-cell proliferation (IC50 = 0.13 nmol/mL) compared to that of chetoseminudin A (IC50 = 0.17 nmol/mL) [95]. The multifaceted immunomodulatory activity of ETPs, particularly the broad immunosuppression mediated by gliotoxin, underscores their potential as candidates for treating immune-related disorders, including autoimmune and immunodeficiency diseases, provided that associated toxicity challenges can be adequately addressed.

5. The Ecological Significance of ETPs

5.1. Role in Fungal-Host Interactions

ETPs serve as critical virulence factors in fungal-host interactions across both plant and animal kingdoms. Their activity is strictly dependent on the oxidized transannular disulfide bridge; reduction or structural modification of this moiety completely abrogates toxicity, underscoring the core structure-function relationship [26,96].
In plant pathogens, ETPs function as dual-purpose molecules, either directly damaging host tissues or manipulating plant defense signaling. For example, sirodesmin PL induces concentration- and time-dependent cell death in Brassica napus cotyledons, with its oxidized form being essential for this activity [97]. It upregulates plant defense-related genes, triggering ROS accumulation, callose deposition, and activation of defense responses. Concurrently, it downregulates photosynthesis-associated genes, reduces photosystem II (PSII) functionality, decreases chloroplast abundance, and disrupts plant energy metabolism and growth, thereby crippling the plant’s capacity for growth and resistance [97]. In contrast, deacetylsirodesmin PL, isolated from Leptosphaeria maculans, acts as an elicitor, triggering phytoalexin biosynthesis (e.g., brassilexin and cyclobrassinin) and increasing levels of stress-related secondary metabolites that enhance plant resistance to subsequent fungal challenge [98].
In animal–fungal interactions, ETPs primarily facilitate infection by suppressing host immunity. Gliotoxin, a key virulence factor produced by A. fumigatus, exemplifies this strategy. Gliotoxin damages immune cells such as macrophages by inducing apoptosis through ROS generation and caspase activation and simultaneously disrupts critical immune signaling pathways by inhibiting NF-κB nuclear translocation [96,99]. Beyond immune suppression, gliotoxin also induces a non-apoptotic, mitochondria-dependent cell death in both the fungus itself and host cells, causing mitochondrial fragmentation and severe functional impairment [96].
Notably, ETP-producing fungi employ sophisticated self-protection mechanisms to avoid self-harm. A. fumigatus, for instance, utilizes a dedicated detoxification system where the oxidoreductase GliT and the methyltransferase GtmA, coordinated by the transcription factor RglT, sequentially inactivate gliotoxin [96]. The evolutionary conservation of these protection mechanisms in even non-ETP-producing fungi suggests they represent a fundamental fungal adaptation to environmental ETP toxicity.

5.2. Competition and Symbiosis in Fungal Communities

ETPs play a role in both competitive and symbiotic interactions within fungal communities. During ecological competition, ETP-producing fungi utilize these compounds to inhibit the growth of rival fungi. For example, Trichoderma produce secondary metabolites such as peptaibols, harzianolides, and gliovirin, which exhibit direct antimicrobial activity and act as chemical signaling molecules to activate plant defense mechanisms. This enhances plant resistance to pathogenic infections, thereby reducing pathogen damage and indirectly weakening the competitiveness of other harmful fungi in the plant ecological niche [100]. Additionally, gliotoxin and dehydrogliotoxin isolated from the endophytic fungus Penicillium sp. of Astragalus membranaceus (Hengshan variety) demonstrated potent inhibitory activity against the powdery mildew pathogen Erysiphe pisi (MIC = 1.56 mg/L and 0.78 mg/L, respectively), outperforming some commercial fungicides (e.g., triadimefon). This suggests that endophytic fungi establish a symbiotic protective relationship with host plants (e.g., Astragalus) through the production of specific metabolites, such as gliotoxin-like compounds [101].
Fungal–fungal coculture technology promotes the discovery of novel natural products by simulating natural ecological competition and thereby activating silent gene clusters to induce the biosynthesis of secondary metabolites [26,100,102]. A representative example is the co-culture of the marine fungi Aspergillus sclerotiorum and Penicillium citrinum, which yields two novel toxins, alumino-neohydroxyaspergillin and ferrocyano-neohydroxyaspergillin [103]. The former exhibits significant selective cytotoxicity against the human histiocytic lymphoma U937 cell line and inhibits the growth of S. aureus [103]. Beyond fungal–fungal systems, fungal–bacterial co-culture also effectively induces bioactive secondary metabolites. For instance, glionitrin A, isolated from the co-culture of Sphingomonas sp. and A. fumigatus in an extreme acid mine drainage environment, demonstrates potent anti-MRSA activity (MIC = 0.78 µg/mL) and submicromolar cytotoxicity against several human cancer cell lines such as HCT-116 and A549 [86]. Further expanding the scope of such interactions, Epicoccum dendrobii has been shown to act as a “donor fungus” that, when co-cultured with fungi including A. nidulans, Penicillium chrysogenum, Fusarium proliferatum, Aspergillus oryzae, and Aspergillus terreus, induces global changes in their secondary metabolic profiles. These changes are mediated by organic small molecules in the fermentation broth of E. dendrobii rather than physical contact, highlighting its potential as a key resource for constructing targeted coculture systems and exploring novel secondary metabolites [102,104].

6. Challenges and Future Prospects

6.1. Challenges in ETPs Research

One of the primary challenges in ETP research is their low natural abundance. Most natural ETPs are isolated from fungi, yet their yields are limited, and the presence of numerous structurally similar analogs complicates purification. For example, ETP derivatives like pretrichodermamide and aspirochlorine require specialized culturing conditions (e.g., seawater-based media, prolonged static fermentation) and are susceptible to environmental influences. Additionally, certain compounds undergo structural transformations during isolation (e.g., light-induced generation of radicals in chetomin analogs, leading to desulfurization and intermolecular disproportionation reactions, resulting in structural modifications [105]), rendering the products unstable. These limitations hinder in-depth investigations into their bioactivity and mechanisms. Furthermore, the intricate architecture of ETPs, including transannular disulfide bonds and polycyclic heterocyclic systems, presents significant synthetic obstacles. Stereochemically complex features such as α, β’-bridging, spiro rings, and 1,2-oxazadecaline units demand elaborate synthetic routes. To date, only a few ETPs (e.g., gliotoxin, aspirochlorine) have been fully synthesized, often with low yields and high production costs [15]. The structural complexity of ETPs poses significant synthetic challenges, underscoring the need for developing efficient synthetic methodologies to produce ETPs and their derivatives.
Another challenge lies in elucidating the intricate regulatory mechanisms of ETP biosynthesis. Many ETP biosynthetic gene clusters encode a greater number of proteins than anticipated, with the functions of some remaining undetermined. For instance, the roles of GliH in gliotoxin biosynthesis remain unclear, and similar uncertainties exist in other gene clusters, hindering comprehensive understanding of ETP biosynthetic pathways [53].
Additionally, the biosynthetic mechanisms of α, β’-bridged ETPs (e.g., gliovirin, epicoccin A) remain incompletely understood despite significant research efforts [26]. The formation mechanism of irregular disulfide bonds in gliovirin and the enzymatic reaction process of epicoccin A require further investigation [26]. Furthermore, current knowledge of dimeric ETP biosynthesis remains limited, including stereochemical transformations during biosynthesis, timing of pairing reactions, reaction mechanisms, and substrate selectivity of dimerizing enzymes. These unresolved questions highlight the need for interdisciplinary approaches to unravel ETP biosynthetic complexity.
The structural diversity of ETPs complicates the correlation between specific structures and bioactivities, making it challenging to rationally design ETPs with tailored bioactivity. This limitation impedes structure-based drug development and deeper exploration of their biological functions.

6.2. Future Research Directions

Future research on ETPs should focus on developing more efficient production strategies. This may involve genetic engineering of ETP-producing fungi to enhance biosynthetic capacity or employing synthetic biology approaches to reconstruct artificial biosynthetic pathways in heterologous hosts. Furthermore, comprehensive investigation of ETP bioactivities is required to identify novel biological targets and elucidate their detailed molecular mechanisms, which could provide crucial directions for developing innovative therapeutic agents.
From an ecological perspective, additional studies are needed to fully understand the roles of ETPs in fungal-environment interactions, including their participation in fungal communication, competition, and symbiosis. Additionally, the development of novel analytical techniques for detecting and quantifying ETPs in complex environmental samples is essential for investigating their natural distribution and ecological functions.

7. Conclusions

Natural products have consistently served as an essential source for drug discovery and development. Their extensive structural diversity, favorable biocompatibility, and well-defined pharmacological effects enable them to address key therapeutic areas, such as anticancer and antimicrobial activity, thereby providing continuous inspiration and material for pharmaceutical innovation. As a structurally distinct class, ETPs are characterized by a unique thio-bridged dioxopiperazine scaffold modified through diverse patterns, further illustrating the remarkable potential for structural diversity among natural products. ETPs not only demonstrate broad application prospects in medicine, agriculture, and environmental science but also play significant ecological roles. Despite common challenges in natural product research, including difficulties in screening active constituents and complexities in optimizing drug-like properties, continued and in-depth investigation of ETPs is expected to unlock their full application potential. Such efforts will also provide novel insights into foundational fields such as fungal biology and natural product chemistry, thereby promoting the broader translation of natural product value across multiple disciplines.

Author Contributions

Q.Z., M.J. and P.Z. conceived and designed the manuscript. H.L., T.S., Y.X., T.Z. and L.Z. supervised the project and critically appraised the manuscript. Q.Z., M.J., X.X. and P.Z. reviewed and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Natural Science Foundation of Shandong Province (No. ZR2022QC186), Key R&D Program of Shandong Province, China (No. 2024TZXD067, 2022SFGC0105), Young Taishan Scholarship to Xuekui Xia (No. tsqn202103100), and Key Innovation Project of Qilu University of Technology (Shandong Academy of Sciences) (NO. 2025ZDZX14).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
ETPEpipolythiodioxopiperazines
DKPDiketopiperazine
NRPSsNonribosomal peptide synthetases
FDAU.S. Food and Drug Administration
ROSReactive oxygen species
IC50Half Maximum Inhibitory Concentration
MICMinimum Inhibitory Concentration

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Figure 1. A generalized common structure found within ETPs.
Figure 1. A generalized common structure found within ETPs.
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Figure 2. Structures of ETPs. (A) α, α’-disulfide bridged ETPs including gliotoxin [16], sirodesmin PL [17], acetylaranotin [18], and sporidesmin A [15,19]. (B) α, β’-disulfide bridged ETPs including pretrichodermamide A [9], aspirochlorine [20], lasiodipline D [21] and gliovirin [22].
Figure 2. Structures of ETPs. (A) α, α’-disulfide bridged ETPs including gliotoxin [16], sirodesmin PL [17], acetylaranotin [18], and sporidesmin A [15,19]. (B) α, β’-disulfide bridged ETPs including pretrichodermamide A [9], aspirochlorine [20], lasiodipline D [21] and gliovirin [22].
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Figure 3. (A) Module and domain structure of NRPS [38]. (B) Biosynthesis of the cyclic dipeptide scaffold by NRPSs.
Figure 3. (A) Module and domain structure of NRPS [38]. (B) Biosynthesis of the cyclic dipeptide scaffold by NRPSs.
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Figure 4. Current reaction scheme for the biosynthesis of gliotoxin.
Figure 4. Current reaction scheme for the biosynthesis of gliotoxin.
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Figure 5. Different post-modified structures of ETPs: gliotoxin [51], aspirochlorine [17], sirodesmin PL precursor [4] and prespiro-aspirochlorine [50].
Figure 5. Different post-modified structures of ETPs: gliotoxin [51], aspirochlorine [17], sirodesmin PL precursor [4] and prespiro-aspirochlorine [50].
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Zhang, Q.; Jia, M.; Li, H.; Shi, T.; Xu, Y.; Zhao, T.; Zhang, L.; Zhao, P.; Xia, X. Epipolythiodioxopiperazines: From Chemical Architectures to Biological Activities and Ecological Significance—A Comprehensive Review. Fermentation 2025, 11, 700. https://doi.org/10.3390/fermentation11120700

AMA Style

Zhang Q, Jia M, Li H, Shi T, Xu Y, Zhao T, Zhang L, Zhao P, Xia X. Epipolythiodioxopiperazines: From Chemical Architectures to Biological Activities and Ecological Significance—A Comprehensive Review. Fermentation. 2025; 11(12):700. https://doi.org/10.3390/fermentation11120700

Chicago/Turabian Style

Zhang, Qingqing, Mingyang Jia, Hongyi Li, Tingting Shi, Ying Xu, Taili Zhao, Lixin Zhang, Peipei Zhao, and Xuekui Xia. 2025. "Epipolythiodioxopiperazines: From Chemical Architectures to Biological Activities and Ecological Significance—A Comprehensive Review" Fermentation 11, no. 12: 700. https://doi.org/10.3390/fermentation11120700

APA Style

Zhang, Q., Jia, M., Li, H., Shi, T., Xu, Y., Zhao, T., Zhang, L., Zhao, P., & Xia, X. (2025). Epipolythiodioxopiperazines: From Chemical Architectures to Biological Activities and Ecological Significance—A Comprehensive Review. Fermentation, 11(12), 700. https://doi.org/10.3390/fermentation11120700

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